It is probably not that "windows" wont display, but your monitor may not be able to handle 1024x768. Is it a 15" montor?

Anyway, usually you can undo this by going into Safe Mode and going in to the display panel and set the setting you want.
You can also go into Safe Mode and go to Start-Run and type "msconfig" and then to Advanced I think (for 9x OS). In there is an option for low video settings.

To get to Safe Mode, press F8 on the keyboard BEFORE the Windows logo shows up. Best way is to just press it over and over until you get the menu.